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Blog Entries posted by running_dry

  1. running_dry
    So in my last post I promised to follow up by talking about why humans can run so far, but I'm putting that off for a little bit.

    So I was just sitting here, daydreaming about everything I've done this XC season, and I suddenly realized how long it's been since the last time I went out and did my first true love: longboarding. I got into longboarding in 5th or 6th grade, I can't really remember, and its not an understatement to say that it has been a focal point of my life; but I haven't touched a board since August in fear of hurting myself and not being able to run (which I now realize was dumb).

    So as I think about tearing down Thomas Ave. at 30+ mph, the physics applications of longboarding seem limitless. But for now I'll talk about sliding and freeride. Sliding on a longboard is actually just what it sounds like: making the board slide downhill (or on flat ground with enough speed) rather than roll. The concept is simple enough: shift weight on the board to apply enough force to get the wheels to break static friction with the road, but in practice this requires much skill, balance, and knowledge of the slide characteristics of your board setup (which is found "experimentally"). Most of the time longboard wheels rely on static friction to allow the wheels to stick to the road while turning, but with sliding its all about the slip. And not just any slip will suffice; while the goal is to get wheels to have less friction with the road, too little friction can be a bad thing. Too little friction will create fast, loud, uncontrollable slides, and wheels that create these kind of slides are known as being "icy", while wheels with pleasant, quiet, controllable slides are referred to as "buttery" or even "sugary". One of the downsides of sliding polyurethane wheels across the road is that they wear down over time as the urethane wears down. Since more pressure is put on the outer edge of the wheel the outer edge wears more and wheels usually become conical over time. With some wheels you can even see what wore off on the road, and these marks are known as thane lines. There are many forms of sliding and those who master the slide master friction itself.

    Sergio Yuppie demonstrating technical downhill sliding (with some freeride, skip to 1:00 for the skating)

    Some sweet freeride

    World record longest standup slide on dry pavement (skip to 2:25 for the actual slide)

  2. running_dry
    So in case nobody noticed, a few days ago the temperature dropped from levels typical of mid-June to somewhere off the charts that I would estimate to be pretty darn close to absolute zero. Actually, the temperature is now just slightly below the average for the season, but why did it get really cold really fast? To start, I'm sure the jet stream had something to do with it, pushing cold arctic air into upstate NY, and pushing out the warmer tropical air we had been experiencing. But more importantly, its now late October and it gets cold around this time every year. But why is that? First of all, the earth rotates on a tilted axis; so in other words the axis on which the earth spins is not perpendicular to the plane on which path of earth's orbit around the sun lies. The ends of the axis of rotation are the geographical north and south poles, not to be confused with magnetic poles. As the earth travels in a slightly elliptical path around the sun, the geographical north pole always points in the same direction in space, so during the summer in the northern hemisphere the pole is pointing in the general direction of the sun while in the winter the pole is pointing away from the sun. As a result, the angle at which the sun's rays strike the earths surface is closer to 90 degrees and less light waves are reflected into space, causing more energy to strike the earth, causing the temperature to rise. The opposite happens in the winter, and this is the reason why it is summer in the northern hemisphere while it is winter in the southern hemisphere. Therefore, the reason why it got cold is because light isn't hitting the earth like it used to. For a visual representation of this, watch this video.

  3. running_dry
    There is one thing that can strike fear into the heart of any cross country runner: hills. Hilly courses are often hated because going uphill is hard, however for a long time I have been telling myself that what goes up must come down, and running downhill is ridiculously easy. The best example of this that I can think of is the Bowdoin Park course in Poughkeepsie, NY. This is widely regarded as one of the hardest XC courses in the state. It's a 5 km course that winds its way up and then down a large hill. The very top of the hill is exactly the half way mark of the course so there's 2.5 km on the "uphill" section and 2.5 on the "downhill" section, and the start and finish line are at exactly the same elevation. According to google earth there is a 65 meter elevation change from the start/ finish to the 2.5 km mark (although that seems a little low to me). Most runners hate this course because of all the work they must do against gravity in the first half of the race, but they forget that in the second half gravity is doing work on them. For example, since work=force*displacement, a 70 kg runner must do 4550J of work against gravity going uphill, but gravity does 4550J of work on them going downhill so net work (as far as climbing hills goes) for the course is 0 joules. Now obviously not even close to all the energy used running is returned, and running downhill isn't free fall so energy must used by the runner on the way down. Yes, hills are challenging but but I think that people need to stop complaining and accept that during races gravity helps them almost as much as it hurts them.
  4. running_dry
    As a competitive runner, there is nothing more annoying than being passed at the very end of a race, and nothing more satisfying than doing the passing. The final surge of speed before the finish line is commonly referred to as a "kick" and runners who can consistently run the last 100 to 200 meters of a race in a convincingly Usain Bolt-like fashion are known as having "a kick". Getting passed by someone while they are "kicking" faster than you is called being "outkicked" Unfortunately I'm not fast when it comes to raw speed and therefore don't have much of a kick. As a result, I have been outkicked on more times than I care to count, leading to much regret and humiliation. My latest encounter with this phenomenon occurred at the McQuaid Cross Country Invitational last weekend. For 2 3/4 miles I had been fighting myself and a pack of aggressive cross country runners (a bit of an oxymoron...) for second place, and I thought I had broken away. Then, coming down the last hill before the final straight away someone catches up and I hear his coach yell "rock that 52 speed!" I groan inside, now knowing that the guy can run 400 meters in 52 seconds which is very fast, much faster than me. And that's where physics comes in.

    The maximum speed at which a person can run is determined by newtons 3rd law, which states that for every force applied, there will be an equal and opposite reaction force. While running, the foot and leg muscles apply a force to the ground in the opposite direction of the intended direction of travel, and via newton's 3rd law the ground applies an equal and opposite force to the runner, propelling then forward. The reason that my competitor was faster than me was that he was able to apply more force to the ground and therefore receive a greater push forward from the ground. The reaction force received from the ground because of newton's 3rd law is translated to speed by newton's 2nd law which states that net force equals mass times acceleration, or acceleration equals net force divided by mass. Assuming that me and this other runner are about the same mass (because, being runners, we're both unnaturally underweight) the other runner is able to accelerate and run faster than me because he is able to apply more force and is therefore subjected to greater net force in a forward direction. And so, once again, I got outkicked (but on the bright side I still took 3rd in the race).

    This just scratches the surface of the physics of running, so stay tuned for more; but I'll mix it up with some other cooler stuff too.

    ~That dry, boring running guy
  5. running_dry
    So I'll get straight to the point. There has been a lot of talk about insanity and it being crucial to the decisions of all of us to take Physics C, and I think there's some truth to that. I too may be a little insane for taking this class but I think that most people think that I'm completely crazy because I genuinely love running (I don't think that makes me crazy though). Sadly that's most of my life but in my free time I try to do some more exciting things like skiing and longboarding as much as possible. With that said, expect a lot of future blog posts on the physics of running and gravity related sports.

    I'm taking Physics C this year because I aspire to be an engineer of some sort and be involved with something really cool. And the money wouldn't be so bad either. And I'm pretty sure that continuing to learn physics will help me in a college engineering program. Plus I think that physics is more interesting than chemistry and biology...

    I'm really excited to learn some of the physics of the real world, rather than the laws of some unattainable perfect world that we learned in Physics B because that's boring. And lets be real, if the hardware store that was brought up so many times last year (you know that one that sells mass-less rope, friction-less tables, inclined planes and pulleys, and is likely full of resistance-less air) existed, it would put Lowes and Home Depot out of business in an instant. Interestingly enough, as of now I'm not scared of this class, probably due to false hope or ignorance, so I guess I'm anxious to see how that pans out in a few weeks.

    Oh and I'm really tired right now so that's why this post may seem like a half- lucid rant.

    Maybe it's not that simple after all.

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